Liquid crystal displays (LCDs) have been widely used in the mobile displays, notebook computer panels, personal computer (PC) monitors and TVs. Fast response, high contrast ratio, high transmittance and wide viewing angle without color reversal are the main problems for getting high display quality, which is critical in large size monitors and TV applications. As one of the promising candidates, in-plane switching (IPS) mode liquid crystal display has been introduced for getting the high display quality in these areas because of its inherent wide viewing angle properties as described in S. Yeo, A LC Display for TV Application, SID 2004 Digest, (2004), p. 758.
The in-plane switching concept was first published in R. A. Soref, Transverse Field Effects in Nematic Liquid Crystals, Applied Physics Letters, vol. 22, (1973), p. 165 and, Field Effects in Nematic Liquid Crystals Obtained with Interdigital Electrodes, Journal of Applied Physics vol. 45, (1974), p.5466. In 1992, Kiefer et al, In-Plane Switching of Nematic Liquid Crystals, Japan Display '92, (1992), p.547. extended the operating principle to display devices and later Hitachi Japan developed the in-plane switching concept into commercial products. In an in-plane switching liquid crystal display, the electric field is applied in the transversal direction from the pixel electrode and the common electrode which are located on the same substrate. The liquid crystal molecules between the neighboring electrodes are rotated in the same plane. This is why the in-plane switching mode LCD exhibits a wide viewing angle. Unfortunately, the off-axes light leakage of the crossed polarizers at the oblique incident angles deteriorates the wide viewing angle properties of conventional in-plane switching LCDs using the stripe-shaped electrodes. Moreover, since the LC molecules between the electrodes are uni-directionally orientated, a color-shift phenomenon occurs and degrades the image quality when viewed at large incident angles. In addition, the response time of a 4-μm in-plane switching liquid crystal cell is slow, approximately 50 ms when a special driving circuit and proper LC material design.
To solve the off-axes light leakage of the crossed polarizers problem and to widen the viewing angle of the in-plane switching LCDs, J. Chen et al., Optimum Film Compensation Modes for TN and VA LCDs, SID 98 Digest, (1998) p. 315 and Y. Satoh et al., Optimum Film Compensation of Viewing Angles of Contrast in In-Plane-Switching-Mode Liquid Crystal Display, Japanese Journal of Applied Physics, vol. 37 (1998), p. 4822 discloses use of uniaxial films and biaxial films for compensation. However, the results were not very promising.
In an attempt to suppress the shortcoming of the color-shift problem, S. Aratani et al., Complete Suppression of Color Shift in In-Plane Switching Mode Liquid Crystal Display with Multi-domain Structure Obtained by Unidirectional Rubbing, Japanese Journal of Applied Physics, vol. 36 (1997), p. L27, describes use of a zig-zag electrode with a multi-domain structure. A similar solution was disclosed in U.S. Pat. No. 6,266,116, issued to M. Ohta et al on Jul. 21, 2001. A solution for preventing the color shift in in-plane switching LCDs is described in U.S. Pat. No. 6,128,061 issued to Lee et al. on Oct. 3, 2000. The LCD comprises of a rectangular frame main electrode and the dividing electrodes to divide the electrodes into sub-pixels in both the vertical and the horizontal directions.
Recently, a LCD mode that combines IPS and vertical alignment (VA) concepts was described by W. Liu et al., Electro-optical Performance of a Self-Compensating Vertically-Aligned Liquid Crystal Display Mode, Japanese Journal of Applied Physics, vol. 38 (1999), p. 2779 and a similar device configuration was disclosed in U.S. Pat. No. 6,177,973 issued to S. Lee et al. on Jan. 23, 2001. The in-plane field can incur the deformation transition of vertical alignment and the liquid crystal molecules with the positive dielectric anisotropy can be used. It has the advantages of fast response and wide viewing angle ability when used in conjunction with the appropriate compensation films.